Many laser-processing schemes rely on beam delivery via an optical fibre. This fibre is usually radially symmetric (of circular cross-section) and has a uniform refractive index profile (otherwise known as step-index). The beam emitted from such a fibre is thus also circularly symmetric and produces a generally uniform distribution of light on a workpiece receiving a laser beam via the beam delivery optical fibre.
For many applications it is desirable to produce tailored non-uniform light distributions on the workpiece, such as an annular profile or profiles having a central peak. Schemes are available for producing such profiles but are often complex and involve the use of free-space optics. The use of these is undesirable, particularly with high-power fibre-laser systems.
One method of producing high power fibre laser systems is to combine the outputs from several lasers via a tapered fibre bundle, spliced to an output fibre. Each laser is delivered to the bundle via a separate input fibre, the laser beams in the separate input fibres are then combined and all their inputs exit via the same single output fibre. These are known generally as output combiners. One aspect of such a combining scheme is that, although the individual input fibres are located in close proximity to each other, the inputs are distinct while they remain in the tapered bundle. The standard output fibre collects all of the inputs and produces a uniform output as all the inputs are overlapped by the same circularly symmetric single refractive index region.
WO 2011/048398 discloses a system having a tapered input fibre bundle.